The present invention relates generally to operational amplifiers (hereinafter op amps) and more particularly, to such amplifiers which are utilized in circuitry where low level signals are common, for example, digital circuitry.
As is well known in the electronic arts, most op amps generate an offset voltage output when null output conditions exist at the inverting and non-inverting inputs thereof. In fact, op amp manufacturers list this null offset voltage most prominently on their specifications sheets. Although this null offset voltage output presents few problems in circuitry where high level signals are common, such as in servo controllers, it is always a design consideration in other circuitry, for example where an op amp is connected as a comparator in an analog-to-digital converter. As recommended by op amp manufacturers, when this null offset voltage output presents a problem, active compensation therefor is commonly provided by applying a supplemental DC bias equal in magnitude and of opposite polarity to the offset voltage, at the appropriate power input terminal of the op amp. Of course, the energizing power supply or battery arrangement can be modified or a separate battery may be added to provide this active compensation. However, the cost and design complexity is increased significantly as the result of such compensation. Furthermore, such compensation does nothing to preclude the continuous power drain which is inherent to the null offset condition and is very undesirable for battery operated equipment.